Gondan, Raffai, and Frei, in coordination with the
Burst and EBBH Working Groups

We investigate the
astrophysically allowed ranges of parameters of eccentric binary black
holes (EBBHs) in galactic nucleus and in globular cluster environments [D11]. These
parameters include initial eccentricity, masses, and initial pericenter
distance. The aim of this project is to identify the maximum volume and the
source distributions within the parameter space that need to be covered
with a search for EBBH signals. We take into account how much the ranges of
parameters are bound by the fact that stable binaries must form in presence
of many other black holes in the environment, which could disrupt the
formation process. This effect has so far remained uninvestigated in
previous EBBH studies.

We also study the simulated waveforms of EBBH
signals, with the main focus of modelling the arrival times and durations
of GW-bursts in the repeated burst phase of the EBBH waveform evolution [D11]. The aim
of this study is to explore the possibility of reducing the parameter space
to be covered in a search process for EBBH repeated bursts with a
simplified but still sufficiently accurate model of burst timing data. With
such a model, we could directly apply techniques such as the one introduced
in Murphy+ 2013 [R39] developed
to aim repeated bursts from a given astrophysical source.

We have developed an
algorithm that can automatically extract the arrival times and durations of
repeated bursts from EBBH waveforms. Using an extensive set of waveforms
produced by EBBH waveform simulators, we perform statistical studies on the
peak durations of the individual burst events, and on their distances in
time. As the different waveform simulators produce robust timing data for
the repeated bursts, we have an opportunity to develop a search technique
that is practically independent from the exact EBBH models.

Cartoon of the formation process of
an eccentric binary black hole

Searching for repeated gravitational-wave transients

Raffai in coordination with the Burst Working
Group

While working as a
postdoc member of the LIGO group at Columbia University, New York, Peter
Raffai participated in the development of a detection method that aims to
find any type of repeated gravitational-wave burst (GW-burst) signals
emitted by the same astrophysical source. Examples for such astrophysical
sources include soft gamma-repeaters (SGRs) and eccentric binary black
holes (EBBHs).

The detection method was introduced in a paper
published in Physical Review D [R39]. The paper
also introduced a data quality veto method, and presented sensitivity test
results with simulated S5 data, where, as an example, the simulated
repeated GW-bursts were associated with SGR quasi-periodic
oscillations.

Members of EGRG have also investigated the
possibility of applying the search technique in future searches for SGR and
EBBH repeated bursts. As part of this project, we have produced a software
tool [T9] that
projects simulated signals to the output data stream of any chosen existing
(or even hypothetical) GW-detectors. The tool uses the physical parameters
of a simulated GW-source and the GPS time of arrival of the signal, and
calculates the h(t) output for any given GW-detector, using time-dependent
antenna factors (that are necessary to be taken to account for these long
GW-transients). The tool also calculates the antenna factor corrected
projections of individual bursts, providing an opportunity to optimize the
number of such bursts taken to account in the search process in terms of
maximizing signal-to-noise ratio.

Detector background with and without a
simulated data quality step [R39]

An X-ray source catalog for the LIGO X-ray Follow-up
Program

Raffai and Frei, in coordination with the Burst
and EM Follow-up Working Groups

We have constructed a catalog of ~750 000 X-ray
sources that are also possible candidates for producing gravitational waves
in the LIGO-Virgo band (XGWC Catalog) [D7]. The XGWC catalog is
based on public data resources, such as the Master X-ray Catalog of the HEASARC Data
Archive and the Gravitational
Wave Galaxy Catalog. The purpose of this work is to support X-ray
background studies for joint observations (such as in the LIGO Swift Follow-up
project), using current and future X-ray telescopes and GW
detectors.

We have also developed a software tool that is
capable of browsing among the catalog elements using various search
parameters [T8]. The
tool allows source background investigations within proposed observational
tiles of an X-ray telescope. An on-line public version of the catalog and
the search tool is available HERE. The XGWC and the
on-line search tool has already been used in background studies for Swift
observations triggered by LIGO-Virgo GW events [L35], doing prompt
searches for known X-ray sources within the reconstructed Swift
tiles.

Sky distribution of
the XGWC X-ray sources and GWGC galaxies.

Developing a new software for spinning
waveform generation

Tapai and Gergely, in coordination with the CBC
and Spinning Working Groups

The formerly applied algorithm used for spinning waveform generation,
called SpinTaylor, generates precessing spinning waveforms using the fourth
order Runge-Kutta method with adaptive stepsize. We have developed a
similar program, called SpinQuadTaylor, which includes all spin effects (spin-orbit,
spin-spin, self-spin) and the mass quadrupolar effects up to 2PN in the
phase. Thus it is more accurate, and also faster than SpinTaylor, and has a
Doxygen generated
documentation, such that any potential users can have access to
the information about the functions and the parameters it uses. The
software produces inspiral waveforms both for equal and IMR masses, and
they can be trusted also for mass ratios <0.1.

Spinning waveforms generated by the
SpinQuadTaylor algorithm.

Developing
the new waveform family of Spin Dominated Waveforms

Tapai and Gergely, in coordination with the CBC and Spinning Working
Groups

We have developed a new waveform
family for gravitational waves emitted by binary black holes with the
larger component having a mass of 30 to 140 times the mass of the smaller
one. In this mass ratio regime the spin of the larger component dominates
over the orbital angular momentum of the system throughout the inspiral.
Hence the name spin-dominated waveform (SDW) has been introduced [R38].

We started to
develop an SDW generating code, to be implemented in LALsimulation. The
time scale of SDW being in the sensitive band of Advanced LIGO is several
seconds, hence it qualifies as a long GW-transient. We propose to study
whether the STAMP algorithm [R34] is an
effective detection method when searching for SDWs.

Time scale of SDWs in the aLIGO band, as
function of total mass and mass ratio[R38]

DETECTOR CHARACTERIZATION PROJECTS

First sound at GEO600

Frei, Gelencsér, Szeifert,
and Szokoly, in coordination with the DetChar Working Group and the GEO600
Collaboration

Although the critical
components of the detectors are protected by vacuum against vibrations due
to sound waves, several others are not. In March 2009 we successfully
demonstrated at the GEO600 gravitational-wave (GW) detector
site in Hannover, Germany, that sound waves generated outside the detector
chamber indeed show up in the GW detector output [D1][D8]. This so called
"coupling" between the acoustic and gravitational-wave data was
later confirmed by other experiments at GEO600 and at LIGO Hanford. In our
experiments, we used an off-the-shelf subwoofer to generate sound waves,
and monitored the GW data output. The same patterns due to our injections
not only showed up systematically in the GW channel, but also in the data
of two independent microphone devices we used. Although our measurements
only proved that acoustic coupling exists for the GEO600 detector, since
other detectors have very similar design, we concluded that similar results
on coupling are suspected for other detectors as well.

Our group members
taking measurements at the GEO600 detector site.

Spectral densities
of the GW detector output during sound injections, relative to the
background data, where there was no injection. The effect of the 42 Hz
(solid) and 137 Hz (dashed) injections are clearly visible in the spectra,
as well as some harmonics.

Studying infrasound effects in GW
detectors

Szeifert, Raffai, and Gelencsér, in coordination
with the DetChar Working Group

In 2009 we have carried out a series of
experiments at the GEO600 detector site in Hannover, Germany, that proved
that acoustic excitations show up in the gravitational-wave detector
output. As a theoretical follow-up of these experiments, we have studied
the effects of sound waves on ground-based interferometric
gravitational-wave detectors [D8]. In particular, we
put an emphasis on low-frequency sound, based on the fact that at
infrasonic frequencies (a) the environmental noise background in higher due
to a huge number of sources and larger propagation distances; (b) possible
coupling mechanisms have remained uninvestigated in this frequency region;
(c) the low-frequency acoustic noise has not been monitored at the detector
sites; (d) there are recent theoretical models predicting noise sources
(e.g. airplane sonic booms) directly affecting the interferometer test
masses, causing an increased level of the noise background (see Creighton, T., 2008.).

Therefore we have
overviewed all infrasound sources possibly affecting the detectors, and
developed a general model of acoustic coupling to detector components.
Theoretically, the vacuum in current and advanced detectors suppresses the
direct effect of sound waves below the seismic noise level, however several
detector components are outside the vacuum and can directly be affected.
Also, for future instruments, where the seismic noise level is reduced,
there is a chance that sound waves remain the major limiting factor of
noise reduction at low frequencies. Third generation instruments will be
even more affected due to the fact that underground tunnels, where they are
proposed to be built, could amplify sound waves at infrasound frequencies.
We have designed a complex system of infrsound detectors, that could be
used to continuously monitor the on-site acoustic noise background, while
being protected against the effects of local wind noise. We propose to
carry out on-site measurements, experimentally investigating the coupling
mechanisms, and characterizing the on-site acoustic noise.

Theoretically
modeled transmission curves of sound pressure waves affecting the
interferometer test masses in a low-pressure gaseous medium. The
transmission curves are given for various sound frequencies and for a
propagation distance of 1 m.

Development of an infrasound
microphone

Gelencsér, Szeifert, Raffai, Szokoly, and Marton,
in coordination with the DetChar Working Group

We have developed an infrasound microphone device
to monitor on-site low-frequency acoustic noise around gravitational-wave
detectors. Although LIGO is expected to detect gravitational waves at
higher frequencies, possible coupling of infrasound noise to the h(t)
channel so far has not been studied. The basic concept of our device is
quite simple: ambient pressure is measured relative to a pressure reference
inside a small volume. The heart of the system is a completely
self-designed very sensitive differential pressure sensor [D1] with resolution
better than 1 mPa. We tested our infrasonic microphone with a commercial
subwoofer for sound generation to measure the noise background and its
effects to the h(t) channel at the GEO600 detector site. We propose to use
multiple IS microphones for detector characterization as part of the
Physical Environment Monitoring (PEM) system of currently operating and
future detectors [D8].

The heart of our
infrasound microphone: the differential pressure sensor.

Exploring acoustic coupling at LIGO
Hanford

Gelencsér, Raffai, and Szeifert, in coordination
with the DetChar Working Group

To explore and study the possible infrasound
coupling to the gravitational-wave data channel, one of our infrasound
microphones was installed in the LIGO Hanford Observatory in August 2010.
Since then, it has been continuously gathering data, monitoring the on-site
acoustic background. We have developed a complex software tool capable
extracting data from various data channels, and looking for correlations
between them and the microphone data. Correlations are currently being
studied at various times and for various environmental conditions. We
propose to model and report any correlations found between the chosen
channels, in order to understand the underlying mechanisms responsible for
the acoustic coupling we demonstrated previously at the GEO600 site.

Szokoly, Szeifert, Gelencsér, Molnár, Imrek,
Marton, in coordination with the DetChar Working Group

We have developed an alternative data collecting
system for the Physical Environment Monitoring (PEM) system [D1]. It is based on
several different equipments such as DAC boxes, ADC boxes, and universal
data collecting and data transfering embedded computer nodes. The new
design is fully modular, thus, any number of sensors can be easily
integrated without any major effort. This system gives us freedom to use
any kind of sensor with both digital and analog output, or any actuator or
servo. The nodes are connected via 100Base-TX ethernet to the central data
collecting sytem. The nodes are commercial embedded low power boards (NGW100)
running linux. The sensors, DAC boxes, and ADC boxes are connected with
RS-485 bus to a node. In this system the analog voltages are converted to
digital values as near as possible to the source, thus, the effect of EM
and RF noise is minimized beacause the data travels in digital form. In
the future, we propose to implement our board to the existing PEM system of
the LIGO detectors to provide support for the environment monitoring during
the Advanced LIGO era.

Szeifert, Gelencsér, and Raffai, in coordination
with the DetChar Working Group

We have developed a detector characterization
software tool, which is capable of comparing the spectra of the same
Physical Environment Monitoring (PEM) channel or any other LIGO data at
different times. This allows an easy and practical way for tracking changes
in the data, focusing on noise peaks that might appear, changes in
correlation properties or shifts in the data DC level. The tool is proposed
to be included among the standard functions of the LIGO
Data Viewer software package, but an LVC protected on-line version of
the tool is also available HERE, where one can use it
directly by downloading data with given parameters from the Network Data
Server (Sigg, D 1999, LIGO Document T990124-D). The on-line tool is
suitable for providing prompt information on spectral changes to science
monitors or operators working at different detector sites. We are also
planning to use our software tool for monitoring the spectral changes in
the data of our self-developed infrasound microphone device.

Amplitude spectral
densities of a PEM data channel at different times.